1. Technical Field
The present invention relates to a carbon body design for use with electrode joints. More particularly, the invention concerns a unique design for the connecting ends of carbon bodies that facilitates the mechanical locking of electrode joints.
2. Background Art
Graphite electrodes are used in the steel industry to melt the metals and other ingredients used to form steel in electrothermal furnaces. The heat needed to melt metals is generated by passing current through one or a plurality of electrodes, usually three, and forming an arc between the electrodes and the metal. Electrical currents in excess of 100,000 amperes are often used. The resulting high temperature melts the metals and other ingredients. Generally, the electrodes used in steel furnaces are used in electrode columns, that is, a series of individual electrodes joined to form a single column. In this way, as electrodes are depleted during the thermal process, replacement electrodes can be joined to the column to maintain the length of the column extending into the furnace.
Conventionally, electrodes are joined into columns via a pin (sometimes referred to as a nipple) that functions to join the ends of adjoining electrodes. Typically, the pin takes the form of opposed male threaded sections, with at least one end of each of the electrodes comprising female threaded sections capable of mating with a male threaded section of the pin. Thus, when each of the opposing male threaded sections of a pin are threaded into female threaded sections in the ends of two electrodes, those electrodes become joined into an electrode column. Commonly, the joined ends of the adjoining electrodes, and the pin therebetween, are referred to in the art as a joint.
Alternatively, the electrodes can be formed with a male threaded protrusion or tang machined into one end and a female threaded socket machined into the other end, such that the electrodes can be joined by threading the male tang of one electrode into the female socket of a second electrode, and thus form an electrode column. The joined ends of two adjoining electrodes in such an embodiment is referred to in the art as a male-female joint.
Given the extreme thermal and mechanical stress that the electrode and the joint (and indeed the electrode column as a whole) undergo, detachment of the joint and subsequent loss of the electrode column below the detached joint is a recurring problem.
In so-called non-jammed joints, in which the threads of the pin and electrodes, or the two electrodes in a male-female joint, meet on only part of the thread surface, solutions have been proposed to reduce joint stress by affixing the male and female elements of the joint to each other. One method involves melting pitch or another material so that it infiltrates the area between the threads and carbonizes in the heat of the furnace, forming a bond between the joint elements.
For instance, in International application PCT/US02/10125, inventors Pavlisin and Weber disclose a “plug” formed of pitch and expandable graphite. When the plug is placed at the base of an electrode socket, the heat of the furnace causes the pitch to melt and the graphite to expand, forcing the melted pitch between the threads where it carbonizes and locks the joint together. Another joint locking system employed in the past has been to provide one or more holes in an electrode pin at or near each of its ends, and to position pitch in the holes. Again, the heat of the furnace causes the pitch to melt and flow across the threads where it carbonizes and locks the joint in position.
Although effective, these prior art methods for joint locking are maximally effective only in non-jammed threads, such as are illustrated in FIG. 5. In fully jammed threads in which the surfaces of the threads of one element fully contact the surfaces of the threads of the other element, such as those illustrated in FIG. 4, there is insufficient space between the threads for the pitch or other adherent composition to flow there.
There exists a need, therefore, to find a way to reduce the stress between joint elements that works for fully jammed and non-fully jammed graphite electrode joints.